Mmm..i believe the most correct would be "Non avresti dovuto!" ..while the most common is "Non dovevi!" ( In teoria non corretto,ma ultimamente accettato come tale) ,actually if you use the second you'll sound very fluent^^

Gotti wrote:Mmm..i believe the most correct would be "Non avresti dovuto!" ..while the most common is "Non dovevi!" ( In teoria non corretto,ma ultimamente accettato come tale) ,actually if you use the second you'll sound very fluent^^

Thanks very much Gotti!

So I'll stay with "non dovevi".
And if I want to use the other, I'll drop the "fare" and just say:
"non avresti dovuto".